"The data say the presence of the IUD in the uterus stimulates an immune response, and that immune response very, very substantially destroys sperm and keeps sperm from reaching the egg," explained lead researcher Victoria Cortessis. "It stands to reason the IUD might influence other immune phenomenon."

These results could be potentially lifesaving for young adult women who are too old to benefit from the HPV vaccine, said Cortessis. She is an associate professor of clinical preventive medicine at the University of Southern California's Keck School of Medicine.

"The vaccines don't work unless the woman is vaccinated before she's ever exposed to the virus," Cortessis said. "That's why we want 11- and 12-year-olds to be vaccinated, so they have time to be fully vaccinated and have a robust immune response before" first exposure.

Unfortunately, HPV is so widespread that many contract the virus as soon as they initiate sexual activity, Cortessis continued.

"Women in their 20s and 30s and 40s who haven't been vaccinated are not going to be protected," Cortessis said. "That means for decades to come this epidemic of cervical cancer is with us."

However, the study only showed an association between IUDs and a lower risk of cervical cancer. And more research is needed before gynecologists can begin recommending IUDs for protection against cervical cancer, Cortessis and other medical experts agreed.

"It raises the need for further research to be done to see if that is in fact the case," said Dr. Len Lichtenfeld, deputy chief medical officer for the American Cancer Society.

The intrauterine device (IUD) is a small T-shaped object placed inside the uterus to prevent pregnancy. It comes in two types -- one is made of copper, while the other is plastic and emits a small amount of the female hormone progestin.

Cortessis and her colleagues suspected that the IUD might influence risk of cervical cancer because it prevents pregnancy through manipulation of the female immune system.

To explore the theory, the team scoured medical literature for research that measured IUD use and cases of cervical cancer.

The investigators found 16 high-quality studies that could be combined to provide an expanded picture of the risk of cervical cancer for women using an IUD. The data included nearly 5,000 women who developed cervical cancer and just over 7,500 women who did not.

The analysis is "fascinating," and the potential explanation for why an IUD might reduce cervical cancer risk "really does make sense," said women's health specialist Dr. Jill Rabin.

"This is just one more reason potentially to help us recommend a great contraceptive method to women," said Rabin, co-chief of the division of ambulatory care with Women's Health Programs-PCAP Services at Northwell Health in New Hyde Park, N.Y.

But Lichtenfeld was concerned that some of the larger studies included in the analysis dated back to the 1980s and 1990s, when IUDs were being prescribed in the United States to a more select group of women.

Back then, IUDs were not recommended for use in women with two major risk factors for cervical cancer -- multiple sexual partners and a history of sexually transmitted infections, Lichtenfeld explained.

"That becomes a significant factor to consider in evaluating results of this type of study," Lichtenfeld said. "We need more contemporary data and more contemporary study to really answer the question, given those considerations."

But Cortessis said her team took into account individual cervical cancer risk factors such as prior pregnancy, HPV status and number of sexual partners, and found that each of these factors did not affect their bottom-line findings.

Finally, Lichtenfeld said he's concerned that people might use these results as an excuse to forgo regular Pap testing or not get their children vaccinated against HPV.

"That's the risk of folks becoming complacent when they see this type of study," Lichtenfeld said.

The report was published online Nov. 7 in the journal Obstetrics & Gynecology.